When we discuss how free energy changes during a reaction, we're looking at a few important ideas. These ideas help us understand when a reaction will happen naturally, how temperature affects it, and what changes occur in heat and disorder. One important concept here is called Gibbs free energy (G) which helps us figure out if a reaction can happen without needing outside help.

Important Things That Affect Gibbs Free Energy

1. Change in Heat (ΔH):

   • This is about the heat in a system. During a reaction, the heat can change in two ways:
     • Exothermic: This means heat is released (ΔH < 0). An example is burning methane, which lets off heat and usually occurs naturally.
     • Endothermic: This means heat is absorbed (ΔH > 0). For example, when ammonium nitrate dissolves in water, it takes in heat, making ΔH a positive value.

2. Change in Disorder (ΔS):

   • Disorder, or entropy, tells us how mixed up or random things are in a system.
     • If things get more mixed up, ΔS is positive.
     • If things become more ordered, ΔS is negative.
   • Reactions that produce more gas than they use create more disorder. For example, when calcium carbonate breaks down into calcium oxide and carbon dioxide, more gas is formed, increasing disorder.
   • On the other hand, turning gas into solid means losing disorder, leading to a negative ΔS.

3. Temperature (T):

   • Temperature is an important player in figuring out Gibbs free energy. The equation looks like this:
   $$ΔG = ΔH - T ΔS$$
   • In this equation, T is measured in Kelvin. By looking at temperature, we can see how it affects whether a reaction can happen. If ΔS is positive, raising the temperature makes -T ΔS more negative. This can help make ΔG more negative, suggesting the reaction is likely to occur.

What Does Spontaneity Mean?

• A reaction is said to be spontaneous if ΔG < 0. This means the process moves toward a more stable state.
• Examples:
  • Spontaneous Reaction: Rusting of iron (4Fe + 3O₂ → 2Fe₂O₃) happens naturally at room temperature. It has a negative Gibbs free energy because it leads to a stable substance, iron oxide.
  • Non-spontaneous Reaction: Changing graphite into diamond is not spontaneous under normal conditions. This change needs special circumstances, like high pressure and temperature, to happen.

Conclusion

By understanding what affects Gibbs free energy during a chemical reaction, we can learn more about when reactions are likely to happen. The balance between heat changes, disorder, and temperature is really important. By studying these factors, scientists can predict how reactions will go and what conditions are needed. This knowledge is useful in many areas, such as creating new materials, improving industrial processes, and studying living systems.